1. Field of the Invention
The present invention relates to an optical system constituting a viewfinder of a camera and the like.
2. Description of the Prior Art
Various technologies as shown below have been disclosed to improve the performance of an optical system for displaying images. For example, as described in Japanese Laid-open Patent Application No. H8-292371, the entire optical system is formed in one block with a concave back-surface-reflecting mirror comprising an eyepiece optical system and a relay optical system which are integral with each other, thereby reducing the mirror optical system in size and lowering the disposition precision required of the reflecting mirror.
Moreover, as described in Japanese Laid-open Patent Application No. H7-234376, in order to correct the diopter of a picture display apparatus, at least one of the following optical elements is made movable: the display screen of the picture display apparatus; the optical surface of a relay optical system; the optical surface of a decentering correcting optical system; and the optical surface of an eyepiece optical system. Particularly, the reflecting surface of the eyepiece optical system is moved.
Moreover, as described in Japanese Laid-open Patent Application No. H9-222564, as an erecting optical system being compact compared with conventional erecting optical systems, an optical system has, between a principal ray parallelized lens and an eyepiece, two parabolic mirrors substantially sharing the focal point and the axis and being arranged so that the concave surfaces thereof face each other, and an image plane control lens having curvature of field in the vicinity of the focal point thereof.
However, the optical system as described in Japanese Laid-open Patent Application No. H8-292371 is difficult to manufacture because there are a plurality of reflecting surfaces in one block. The optical system as described in Japanese Laid-open Patent Application No. H7-234376 is difficult to adjustment because a reflecting surface which is generally high in error sensitivity is moved. The optical system as described in Japanese Laid-open Patent Application No. H9-222564 is difficult to structure because the reflecting surface is limited to the parabolic surface.